Chemical Pollutants Linked to Fewer Female Births

NEW YORK (Reuters Health) - High exposure to certain now-banned industrial chemicals may lead to fewer female births, a new study suggests.

The findings, reported in the journal Environmental Health, add to evidence that the two groups of related chemicals -- polybrominated biphenyls (PBBs) and polychlorinated biphenyls (PCBs) -- may affect human reproduction.

PBBs were once widely used as flame retardants in plastics, electronic and textiles, while PCBs were used in everything from appliances and fluorescent lighting to insulation and insecticides.

While the chemicals were banned in the 1970s as potential health hazards, they remain a public-health concern because they linger in the environment and accumulate in the fat of fish, mammals and birds.

For the current study, researchers used data from a group of Michigan residents who, in the early 1970s, had been inadvertently exposed to high levels of PBBs; the chemicals had been accidentally mixed into animal feed, leading to human exposure through contaminated meat, eggs and milk.

The researchers observed that, from 1975 to 1988, women in the study group had a higher-than-average rate of male births, relative to the national average.

There was also a suggestion of increased odds of a male birth when both parents' combined PBB exposure was particularly high -- above the midpoint for the study group -- compared with couples whose PBB exposure was lower.

Similarly, couples with high PCB levels had a higher rate of male births.

What this all means for the public at large, however, is unknown, according to lead researcher Metrecia Terrell, of Emory University in Atlanta.

"This was a unique situation, so it's very difficult to extend the findings to people with everyday exposures," she said in an interview.

"Exposure in the general population would be much lower," Terrell pointed out, "and we just don't know if there are effects on sex ratio."